Manufacture of detonating fuse cord

ABSTRACT

DETONATING FUSE CORD HAVING ALONG ITS LENGTH ALTERNATING SECTIONS OF GREATER AND LESSER EXPLOSIVE ENERGY IS MANUFACTURED BY THE CONTROLLED EJECTION OF SLURRIED PARTICULATE EXPLOSIVE INTO A STOCKING AND THEREAFTER DRYING AND COVERING TFHE FILLED STOCKING.

Nov. 23, 1971 WELSH 3,621,559

MANUFACTURE OF DETONATING FUSE CORD Filed Jan. 19, 1970 2 Shoots-Sheet 1INVENTOR David Martin WELSH AGENT Nov. 23, 1971 Filed Jan. 19, 1970 D.M. WELSH MANUFACTURE OF DETONATING FUSE CORD 2 Sheets-Sheet 8 SUPPLY OFEXPLOSIVE PREPARATION OF EXPLOSIVE SLURRY WET FORMATION OF TEX E COVEREDCOLUM EXPLOSIVE DRYING OF WET COLUMN OF EXPLOSIVE EXAMINATION DRIEDTEXTILE CO E E0 COLUMN OF EXPLOSIVE APPLICATION OF MOISTURE BARRIEROPTIONAL FINISHING OPERATIONS INVENTOR David Martin WELSH AGENT UnitedStates Patent 3,621,559 MANUFACTURE OF DETONATING FUSE CORD David MartinWelsh, Brownsburg, Quebec, Canada, as-

signor to Canadian Safety Fuse Company Limited, Montreal, Quebec, CanadaFiled Jan. 19, 1970, Ser. No. 3,861 Claims priority, application Canada,May 6, 1969,

Int. ci. B2255 U.S. Cl. 29420 3 Claims ABSTRACT OF THE DISCLOSUREDetonating fuse cord having along its length alternating sections ofgreater and lesser explosive energy is manufactured by the controlledejection of slurried particulate explosive into a stocking andthereafter drying and covering the filled stocking.

This invention relates to detonating cord and in particular, to themanufacture of a detonating cord having an explosive core of alternatingcore sections of controlled variations. Such a detonating cord hasparticular use in, for example, metal expansion applications.

As is known in the explosives art, detonating cords are normallyproduced in long or continuous lengths and comprise essentially auniform core of explosive encased in a protective wrapping or sheath.Originally, the protective sheath consisted of a soft metal such as leadbut these lead sheathed cords have now generally been superseded bythose having sheaths consisting of Water resistant tape or textilewrappings, synthetic plastics and the like. The amount of explosive perfoot of length in the core may vary from a small quantity of from 0.1 toabout grains, as in low energy detonating cord (LEDC), to as much as 50grains or more. Typical explosives employed as core material are, forexample, pentaerythritoltetranitrate (PETN),cyclotrimethylenetrinitramine (RDX) nitromannite, lead azide,trinitrotoluene (TNT), cyclotatramethylenetetranitramine (HMX), leadstylphnate or tetryl and mixtures of these.

In the explosives industry detonating cords are manufactured by one orother of the dry or wet processes. In the dry process relatively coarse,particulate, dry explosive which comprises the core material of the cordis encased in a continuous column by means of a wrap of tape-likematerial and thereafter encircled by means of textile yarns or the like.The cord may thereafter be coated with a waterproofing surface layer ofpitch, thermoplastic or the like. The dry process is normally employedin the manufacture of detonating cords having a core load of 25 grainsor more of explosive per foot of length.

In the wet process, the core is formed from a thickened aqueous slurryof particulate explosive which is wrapped and covered in much the samemanner as that employed in the dry process. Generally the wet process isemployed in the manufacture of detonating cord having a core load of 4grains or more of explosive per foot of length.

It has heretofore been the object and concern of the explosives industryto manufacture detonating cords having an absolute minumum of core loadvariation throughout the cord length in order to ensure constantdetonation characteristics along the cord, in particular, uniform Ilateral energy output. It has now been found that in 3,621,559 PatentedNov. 23, 1971 to provide a method of manufacture of detonating cordwherein the cord contains a continuous explosive core load, which coreload comprises alternating sections of greater and lesser explosiveenergy.

Other objects of the invention will become obvious from a considerationof the following disclosure and claims.

The novel method of manufacture of the invention comprises the steps ofcontinuously forming a braided textile stocking and directing a streamof slurried particulate explosive through an orifice in a continuouscolumn into said' textile stocking in such a manner that regular,alternating sections of the explosives column within the stocking havedifferent energy outputs.

The method of the invention and the product thereof may be more fullyunderstood by reference to the accompanying drawings wherein:

FIG. 1 is a sectional view of one embodiment of a finished detonatingcord made by the method of this invention;

FIG. 2 is an elevational diagrammatic view, of a portion of theapparatus suitable for use in the method of the invention;

FIG. 3 is an elevational diagrammatic view, partly in section of aportion of an alternative apparatus suitable for use in the method ofthe invention; and

FIG. 4 is a flow diagram of the process steps of the method of theinvention.

Referring in detail to FIG. 1, there is shown a detonating cord 1 havingan inner explosive core 2 which core comprises connected, alternatingthick sections 3 and thin sections 4. Core 2 is encircled by braidedtextile stocking or sheath 5, which sheath has an outer covering 6 of,for example, a flexible thermoplastic material.

Referring to FIG. 2, there is shown pressurized storage containers 10and 11, each containing a quantity of slurried, particulate explosive,for example, PETN. Leading from containers 10 and 11 are delivery lines12 and 13 respectively, which lines terminate at air-operated valve 14.Air cylinder 15 is adapted to operate valve 14. Valve 14 comprises anexit line 16 having an orifice 17 to which the slurried exposive may bedelivered from containers 10 and 11. Below orifice 17 is textilebraiding head 18 by which means a braided textile stocking is formed onorifices 17 and is continuously withdrawn from orifice 17 as it isformed while at the same time the slurried particulate explosive isforced out of the center of orifice 17. Below braiding head 18, thetextile covered cord 1 is delivered to a drying operation (not shown)preparatory to inspection and the application of an outer protectivesheath or coating. Air lines 19 and 20 enter containers 10 and 11respectively and pressurized air (from sources not shown) is directedinto each of these containers. The pressure of the air in container 10is different from the pressure of that of the air in container 11.

Referring to FIG. 3, there is shown an apparatus similar to that shownin FIG. 2 except that the valve 14 and air cylinder 15 of FIG. 2 arereplaced by excentric cam 21 which is rotated by drive means (not shown)to activate pinch valves 22 and 23 which alternatively close off theflow of explosive slurry through lines 12 and 13 respectively.

Referring to FIG. 4, there is shown in sequential steps the variousoperations employed in the method of the present invention.

In one operation of the method of the invention employing the apparatusas shown in FIG. 2, a supply of typical detonating cord explosive, forexample, PETN in suitable particulate form is prepared as an aqueousslurry by combining the PETN grains with a quantity of water and asuitable thickening agent such as, for example, hydroxy ethyl cellulose.A quantity of the PETN/water slurry is placed in each of containers and11 and air pressure is applied to the surface of the slurry in eachcontainer through air lines 19 and 20. Air at, for example, 10 p.s.i. isapplied to container 10 and air at, for example, 40 p.s.i. is applied tocontainer 11. Air cylinder operates valve 14 in timed reciprocatingmotion by well known means (not shown) to allow delivery of theexplosive slurry in alternating sequence from containers 10 and 11 anddelivery 12 and 13 to exit line 16 and orifice 17. As the PETN slurry isforced from orifice 17 and into the braided stocking, it assumes acohesive, string-like configuration having along its length regularlyalternating thick and thin sections. The textile sheathed cord is thenpassed to a drying operation (not shown) and, after inspection, an outercovering of, for example, thermoplastic material is applied. The thuscompleted detonating cord may then be wound on a take-up spool forstorage or shipment.

In the operation of the method of the invention employing the apparatusas shown in FIG. 3, all the steps described heretofore with respect tothe apparatus of FIG. 2 are the same with the exception of the meansemployed to achieve an alternating or pulsating extrusion of the PETNslurry.

Referring to FIG. 3, it can be seen that when excentric cam 21 isrotated by a drive means (not shown) the flow of explosive slurrythrough line 12- and 13 is interrupted in a sequential manner by pinchvalves 22 and 23 thus permitting the extrusion of the explosive slurryat orifice 17 in a column of thick and thin sections.

In the operation of the method employing either the apparatus of FIG. 2or FIG. 3 and using a PETN explosive of grain size normally used for themanufacture of detonating cords of 4 grains or more of explosive perfoot of length containing a small percentage of water and thickener, ithas been found that air pressure of about 10 p.s.i. on container 10 or11 produces a detonating cord section containing an average explosiveload of 24 grains per foot of length when the orifice 17 has an internalcross section of 0.166 inch. An air pressure of about 40 p.s.i. producesan average core load of 52 grains of explosive per foot of lengththrough the same orifice. Employing air pressure of 10 p.s.i. incontainer 10 and 40 p.s.i. in container 11 therefore producesalternating core loads in a continuous length of detonating cord of 24and 52 grains per foot respectively. These core sections of greater andlesser quantity of explosive which take the form of thick and thinsections of core load may be any length as desired since the sectionlength is a function of the length of time the slurry is permitted toflow from the alternative sources of supply. It will be obvious that thequantity of explosives in each of the thick and thin sections of thedetonating cord can be varied depending on the thickness or density ofthe explosive slurry and on pressure of the air delivered to each of thestorage containers. Too thin a slurry will generally result in anunsatisfactory product.

It will be obvious from the foregoing description that detonating cordcomprising alternating connected sections of greater and lesserexplosive energy may also be produced through the use of, for example,explosives having dilferent energy values or strengths. That is to say,the continuous column or core may comprise, for example, a section ofPETN adjacent to a section of TNT with the sequence thereafter repeated.It will also be obvious that a combination of quantities and kinds ofexplosives may be used in the alternating core. For example, one sectionmay comprise a core load of, say, 50 grains per foot of PETN and theadjacent section may comprise, say 25 grains per foot of TNT, or viceversa. The production of such cords using the apparatus shown in thefigures of the drawing may be readily accomplished by placing a selectedslurry of PETN in container 10 and a selected slurry of TNT in container11. Application of appropriate air pressure to each container willprovide extruded sections through orifice 17 of explosive of alternatingexplosive energy. Similarly the explosive adapted for use in the cordsection of lesser energy may comprise a useful particulate explosivesuch as PETN mixed with an inert adulterant in order to further reducethe actual quantity of explosive present in the cord section and hencealso reduce the explosive energy upon detonation of the cord.

It will be appreciated that a wide variety of slurriable particulateexplosives and mixtures thereof may be utilized for the processdescribed.

EXAMPLE To demonstrate that the detonating cord made by the method ofthe invention comprises areas of greater and lesser explosive energy,the following procedure was followed. A detonating cord similar inconfiguration to that shown in FIG. 1 of the drawing was prepared by themethod hereinbefore described and the apparatus of FIG. 2 wherein theareas of lesser cord diameter contained 24 grains of PETN per foot oflength and the areas of greater cord diameter contained 52 grains ofPETN per foot of length. A length of this detonating cord was locatedalong the central radial axis of a cold drawn Inconel (registeredtrademark) steel alloy tube having an outside diameter of 0.75 inch anda wall thickness of 0.056- inch. The open ends of the tube werestoppered after the space between the detonating cord and inner wall ofthe tube was filled with water. The cord was initiated by means of anelectric blasting cap and the degree of expansion of the tube was thenmeasured at points along its length. The tubing sections adjacent the 52grains per foot sections of the cord were found to have expanded to anaverage diameter of 1.005 inch, an increase in diameter of 0.255 inch.The tubing sections adjacent the 24 grains per foot section of the cordexpanded to an average diameter of 0.875 inch, an increase of 0.125inch. Thus it could be seen that the cord of the invention comprisedalternating areas or sections of greater and lesser explosive energy asmeasured by the expansion of the metal tube.

From the foregoing example it can be seen that the detonating cordproduced by the method of the invention may be employed, for example, toexpand a metal tube within a tube sheet where the tube apertures are ofstepped, tapered, or uneven configuration. The expansion of a tubewithin both the narrower access or neck of the tube sheet aperture andthe larger or wider area of the aperture by conventional mechanical tubeexpansion means is not possible. The detonating cord made by the processof the present invention, however, may be usefully employed for suchpurposes by the judicious location within the expandable tube of adetonating cord having alternating sections of dilferent explosiveenergy. Additionally, such a cord may be employed for purposes ofexpanding tubes into tube sheets by the method disclosed by Irwin Bermanet al. in United States Pat. No. 3,411,198 granted Nov. 19, 1968.

I claim:

1. A method of continuously producing detonating fuse cord having alongits length regular alternating sections of different potential energyoutputs comprising the steps of:

(a) continuously forming a braided textile stocking;

(b) continuously ejecting a stream of slurried particulate explosive inregularly varying amounts through an orifice and into said textilestocking, thus forming into said stocking a continuous column ofexplosive having regularly alternating thick and thin sections; (c)drying the filled, braided stocking; and (d) covering the dried, filled,braided stocking with a protective sheath.

2. A method as claimed in claim 1 wherein the stream of slurriedexplosive is ejected by pneumatic force.

3. A method as claimed in claim 1 wherein the par- 3,318,242 5/1967Griffith 102-27 X ticulate explosive is selected from the groupconsisting of 3,367,266 2/ 1968 Griffith 102-27pentaerythritoltetranitrate, cyclotrimethylenetrinitramine, 3,382,8025/1968 Prior et a1. l02-27 nitrornannite, lead azide, trinitrotoluene,cyclotetramethyl- 3,435,764 4/ 1969 Kelly et a]. 102-27 enetetranitramine, lead stylphnate, tetryl and mixtures of 5 th JOHN F.CAMPBELL, Primary Examiner References Cited v. A. DIPALMA, AssistantExaminer UNITED STATES PATENTS US Cl XR 1,275,001 8/1918 Dormer 102-2710 R 1,674,773 6/ 1928 Fritzsche 10227

